Treatment of environmental pollutants with mineral ores

ABSTRACT

A method for removing a pollutant from emissions or the environment comprising: contacting a mineral ore or the use of a mineral ore selected from the group consisting of bauxite, modified bauxite and mixtures thereof. Typically, the pollutant is a heavy metal or a microorganism.

This application claims the benefits of U.S. Provisional PatentApplication No. 60/363,693, filed Mar. 12, 2002; and U.S. ProvisionalPatent Application No. 60/396,526, filed Jul. 17, 2002. The entire textand drawings of the above mentioned provisional applications are herebyincorporated herein by reference as if completely rewritten herein.

FIELD OF THE INVENTION

The present invention discloses the use of several relatively rawmaterials including bauxite, iron ore (e.g. magnetite, hematite,goethite), feldspar, lignite and mixtures thereof for the ameliorationof environmental pollutants and/or emissions. Typical pollutants in theemissions or the environment Include heavy metals such as arsenic,cadmium, chromium, nickel, mercury; microorganisms; organic solvents;and the like.

BACKGROUND OF THE INVENTION

Pollutants in or on the ground, or in surface or ground waters pose anincreasing threat to the environment. The pollutants may result fromindustrial discharges, accidental spills, mine drainage, mine tailingseepage or leaks and the like. Typically, large quantities of pollutedmaterials need to be treated so that cost of the treating materialsbecomes an important factor. The present invention seeks to answer thisneed by using low cost, readily available materials to bind thepollutants.

Heavy metals, such as mercury, arsenic, cadmium, chromium, and selenium,are used in a number of manufacturing operations and industrial andconsumer products, but are hazardous to human health and the ecosystemwhen released to the environment. Often, heavy metals have to be removedfrom gas, water, or soil streams exiting a manufacturing facility orfrom the environment where they have already been released. The currentinvention proposes the use of bauxite or modified bauxite for removal ofheavy metals from fluid streams (gases e.g. air or exhaust gas, liquidse.g. water), and soil or other aggregate material.

A number of different treatment processes and products have beenproposed in the past for removal of these metals from the targetmatrices to prevent the metals from migrating to potential points ofhuman exposure and to protect the environment. In gas streams (forexample, consisting of coal-burning power plant emissions), metals areremoved by using an adsorbent or catalyst. Activated carbon (Vidic R.D., Liu, W. (1997) Development of Novel Activated Carbon-BasedAdsorbents for Control of Mercury Emissions From Coal-Fired PowerPlants. DOE-NETL publication; Miller, S. J., Dunham, G. E., Olson, E.S., and Brown, T. D. (2000) Fuel Processing Technology 65/66:343-363;U.S. Pat. No. 6,402,813 B2) and noble metals, like molybdenum, cobalt,have been used in the past for their adsorptive and catalyticproperties, respectively. A two-step process of oxidation of elementalmercury to a mercury compound, followed by its removal on an adsorbent(e.g., activated alumina) has previously been proposed (U.S. Pat. No.5,607,496). More complex filters, for example those that involve asupport material on which are synthetically deposited multiplecomponents to address multiple pollutants, have also been proposed (U.S.Pat. No. 5,212,131).

Bauxite has sometimes been used in the past for treatment of pollutantsin gases, often after expensive processing to a substance calledactivated bauxite. Activated bauxite is commonly generated by heatingthe bauxite to a temperature in the range from 400 to 1,000° C., inorder to increase its surface area and improve adsorption. For example,U.S. Pat. Nos. 5,595,954 and 4,639,259 describe how activated bauxite oractivated alumina (a purified form of bauxite) can be promoted by addingan alkali metal oxide to remove HCl from fluid streams. U.S. Pat. No.4,973,459 describes the use emathlite and bauxite as sorbents forremoving alkali from hot gases at temperatures up to 1,800° F., by usingthe sorbents in conjunction with coarse particulate materials and filterunits in a moving bed. U.S. Pat. No. 4,865,629 describes a process forflitering fine particulates from a stream of hot gas by blending afraction of particles removed by the cyclones back to the gas; this workmentions the use of diatomite or bauxite particles that can be blendedinto the gas stream to remove corrosive sodium and potassium vapors.U.S. Pat. No. 3,917,733 describes a two-step process for removinghalogen-containing chemicals from a liquid hydrocarbon stream by usingalumina or bauxite as adsorbents, and then using the spent liquid-streamadsorbents as adsorbents for treating gas streams. In all theseapplications, bauxite in an activated form (following heat treatment to400° C. or above) is used primarily as an adsorbent, rather than in araw or gently modified form as a catalyst to cause transformations ofthe target gas stream.

Many of these previous processes suffer from one or more of thefollowing limitations:

-   1. The use of the reagent generates a waste product that interferes    with its eventual reuse or disposal.-   2. The reagent is too specific towards one or other target pollutant-   3. A two-step process is required to obtain adequate removal of the    pollutant metals. This increases the complexity of the process and    cost of the treatment.-   4. The reagent is relatively expensive and economic use of the    reagent requires another process to regenerate and reuse the    reagent.

The present invention addresses these limitations. The inventionconsists of a reagent that is commonly available, removes multiplepollutants, is relatively cheap and can therefore be disposed of after asingle use.

BRIEF DESCRIPTION OF THE INVENTION

A process for treating gas, water, or soil containing heavy metals toprevent their migration in the environment is disclosed. The processinvolves contacting the heavy metals with a multi-functionalsequestration agent, namely, bauxite or modified bauxite. Bauxite isused in its relatively natural form (except for appropriate sizereduction to fit a particular application) or in modified form (forincreased efficiency). Modifications to the raw bauxite include, but arenot limited to, simple processes, such as wetting with water, mildheating to temperatures below 300° C., and/or soaking in solutions ofcommon acids, bases, or salts. In the current invention, when bauxite isapplied for treatment of gases, sulfur is an essential ingredient in theco-precipitation of pollutant metals as sulfides. The sulfur may alreadybe present in the gas stream being treated (as in coal combustion gases)or it may be introduced into the treatment with the bauxite. Whenbauxite is applied to water or soil environments, sulfur is not anessential ingredient for removal of metal pollutants. An importantfeature of the current invention for treatment of air, water, or soilmatrices, is that bauxite, being a relatively cheap material, is used asa single use reagent. No regeneration or reuse of the bauxite isrequired and the economics of the process promotes its single use anddisposal.

The relatively unrefined raw minerals bauxite, iron ore (e.g. magnetite,hematite, goethite), feldspar, and lignite are used for in-situtreatment of is pollutants to clean up surface and subsurfaceenvironments, such as groundwater, soil, fractured rock, surface water,and sediments. These minerals, in their naturally occurring form, areenvironmentally benign, commonly available, and relatively inexpensive.

Other embodiments of the invention provide for the treatment emissionscontaining microorganisms or for the in-situ treatment of pollutants inor on the ground that contain microorganisms. Typically themicroorganisms of interest are pathogenic. Treatment typically consistsof contacting the emissions or contaminated site with the mineral oresdescribed herein.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram depicting the use of bauxite to removepollutant metals from combustion gas. In FIG. 1, ESP refers to anelectrostatic precipitator.

FIG. 2 is a graph that shows the results of a test run for removal ofmercury form a gas stream using bauxite.

FIGS. 3( a) and 3(b) are schematic diagrams depicting the treatment ofground water pollutants using a permeable barrier consisting of bauxiteThe bauxite can be either be placed as granular material in a trench, orinjected as a powder into deeper aquifers.

FIG. 4( a) shows the mixing of bauxite with surface soils to sequesterpollutants. FIG. 4( b) shows the placement of bauxite on top ofcontaminated sediments to prevent migration of pollutants to the waterbody above.

FIG. 5 shows that the pollutant removal of bauxite can be sustained longenough for the treatment to be economical.

DETAILED DESCRIPTION OF THE INVENTION AND BEST MODE

Broadly the invention include a process for treatment of heavy metalsusing a multi-functional sequestration agent.

One embodiment of the Invention consists of the use of bauxite, a commonaluminum ore material, for sequestration of pollutant metals fromgaseous phase (like flue gas), aqueous phase (surface water orgroundwater), and solid phase (like soil or subsurface materials). Thebauxite is used as its natural form or in a modified form that stillretains the essential character of the bauxite. Modifications mayinclude, but are not limited to, simple processes, such as wetting withwater, mild heating to temperatures below 300° C., and/or soaking insolutions of common acids, bases, or salts. The modifications in thecurrent invention aim to primarily increase the reactivity or catalyticproperties of the bauxite, not necessarily its surface area (surfacearea enhancement is generally the goal of common heat treatments at 400°C. or higher that result in the manufacture of products called activatedbauxite or activated alumina). For example, wetting with water enhancesthe reactivity of the bauxite (without increasing its surface area) bydepositing hydroxyl ions on the bauxite surface.

In the case of gaseous streams, an additional essential ingredient inthe current invention is the presence of sulfur. The sulfur may alreadybe present in the target gas stream or may be introduced into thesequestration process, either through the gas stream or through additionto the bauxite. The sequestration of pollutant metals onto the reagent(bauxite) occurs through a combination of sulfide co-precipitation andadsorption.

In the case of pollutant metals in a water environments, bauxite worksthrough a combination of co-precipitation and adsorption of the metalsthat come into contact with it. Even in soil or sediment (freshwater ormarine) environments, the sequestration of pollutant metals occursthrough migration of water through the soil or sediment, as the waterenables the contact between the metals and the bauxite.

Broadly the invention also discloses use of the mineral ores such asbauxite (an aluminum ore), magnetite (an iron ore), hematite (an ironore), goethite (an iron ore), feldspar (a Na—Al-silicate), or lignite,and mixtures thereof for the in situ treatment of pollutants to clean upsurface and subsurface environments, such as groundwater, soil,fractured rock, surface water, and sediments. The pollutants may bedissolved or carried by surface or subsurface water. These minerals, intheir naturally occurring form, are environmentally benign, commonlyavailable, and relatively cheap.

The challenge with in situ (within or adjacent to the affectedenvironmental medium) treatment of pollutants is to find treatmentagents that are relatively inexpensive (that can be spread over apotentially large affected region), commonly available, and arecompatible with the environment. The idea of using raw minerals in theirnaturally occurring form (without much prior processing) takes advantageof the fact that these minerals came from the environment and will begoing back to the environment; this would create less of a regulatoryconcern. The three minerals bauxite, magnetite, and hematite were testedbecause they contain natural oxides or iron, aluminum, manganese,titanium and other oxide compounds, that can potentially react withtransported pollutants, (e.g. heavy metals such as arsenic and mercury,and organic compounds), and prevent them from migrating towardspotential receptors (such as drinking water wells, aquatic ecosystems,etc.). These three minerals are easily available in the United Statesand other countries in bulk; they are either mined in the country or, asin the case of bauxite, mined outside the country but consumed in largeenough quantities, that they are available at reasonable cost. Otherminerals useful with the invention include goethite, feldspar, andlignite. Typically, feldspar and lignite are contemplated for removal ofmercury. Minerals, such as these, contain a variety of constituents thatcan react with pollutants and either adsorb or destroy them.

EXAMPLE 1

The first pollutant that was tested was arsenic. There is a great dealof interest in arsenic, especially because a reduction in the regulatorylimit for this pollutant in drinking water has recently been made. Thelimit (health standard in the U.S.) for arsenic in drinking water hasbeen reduced from 50 μg/L to 10 μg/L.

The Table 1 shows the results of several batch tests. Batch tests wereconducted in small bottles containing a locally obtained groundwater.Arsenic was spiked into the water to levels of approximately 1,400 μg/L.The results show that arsenic levels in the water were reduced fromapproximately 1,400 μg/L to between about 19.8 μg/L and 86.4 μg/L whenthe mineral was added to the water and shaken on a shaker table for 24hours. Nitrogen was bubbled through the water before the tests in orderto remove dissolved oxygen and maintain the arsenic as As (III), versusAs (V). The lower-valent arsenic is more difficult to treat and wasconsidered a greater challenge for the test. The bottles were filled tothe top with little or no headspace. After shaking, the bottles werecentrifuged to settle out the mineral. The supernatant was thenanalyzed. The results are in the Table 1 below.

TABLE 1 Treatment with raw minerals for groundwater containing arsenicArsenic Concentration Test Sample (μg/L) Removal Initial Arsenic 1,350 —Concentration 1* Initial Arsenic 1,420 — Concentration 2* Magnetite,Repetition 1 76.9 94% Magnetite, Repetition 2 86.4 94% Hematite,Repetition 1 36.4 97% Hematite, Repetition 2 20.9 99% Bauxite,Repetition 1 20.0 99% Bauxite, Repetition 2 19.8 99% *Pre-treatmentconcentration in the groundwater was approximately 1,400 μg/L of arsenic(as arsenite). Control runs were bottles without the mineral (justgroundwater and arsenic).

Table 1 indicates that bauxite was the most efficient at removingarsenic, followed by hematite and magnetite. All three minerals achievedgreater than 90% removal of arsenic (all % used herein are in weightpercent). Natural minerals are a complex mix of chemical compounds. Notwishing to be bound by theory, it is presently thought that thecompounds that have played a role in the adsorption and removal ofarsenic from the groundwater were the mix of oxides of iron, aluminum,manganese, and titanium. However, other mineral constituents may haveplayed a role in the removal as well.

EXAMPLE 2

Table 2 shows a second series of tests that were conducted to furthertest the performance of the minerals. Specifically, the two objectivesof the second series were to: (a) determine whether the minerals canremove arsenic to the low levels required by the imminent new regulatorystandard of 10 μg/L, and (b) to determine whether the arsenic would staysequestered by the mineral or would re-dissolve over time. The targetinitial amounts of arsenic (as As [III]) that were spiked intogroundwater were 100 μg/L, 50 μg/L, and 25 μg/L. The correspondingcontrol bottles (no mineral phase added) showed 85.7 μg/L, 40.8 μg/L,and 20.1 μg/L respectively, after one day of mixing. After one day ofmixing, the bauxite appeared to be the most efficient in arsenicremoval, removing the arsenic present in the groundwater in all sixbottles to less than 10 μg/L of arsenic, which is both the imminentregulatory standard and the present analytical detection limit.

TABLE 2 Treatment of varying initial dissolved concentrations of arsenicwith minerals Initial Concentration Day 1 Day 2 Removal Mineral (μg/L)(μg/L) (μg/L) (%) Bauxite 85.7 <10 <10 >88.3% <10 <10 >88.3% 40.8 <10<10 >75.5% <10 <10 >75.5% 20.1 <10 <10 >50.2% <10 <10 >50.2% Magnetite85.7 27.3 12.2 68.1% to 85.8% 26.0 12.4 69.7% to 85.5% 40.8 13.2 <1067.6% to >75.5% <10 <10 >75.5% 20.1 <10 <10 >50.2% <10 <10 >50.2%Hematite 85.7 38.4 36.4 55.2% to 57.5%

When the bauxite test bottles were shaken (mixed) for one more day,there were no signs that any of the sequestered arsenic was desorbed orotherwise released from the solid mineral. The same was true formagnetite and hematite, after two days of shaking.

Hematite and magnetite were not as efficient as bauxite under allconditions, but still removed between 55% to over 99% of the arsenicunder some conditions. All three minerals reduced arsenic to below 50μg/L, the current regulatory limit.

Raw bauxite ore typically contains varying proportions of aluminum oxide(35% to 65% as gibbsite, boehmite, and/or diaspore), silica (0.5% to 10%as quartz and/or kaolinite) and iron oxide (2% to 30% as goethite,hematite, and/or siderite), titanium oxide (0.5% to 8% as anastasiteand/or rutile), and calcium oxide (0 to 5% as calcite, dolomite, and/ormagnetite). Again not wishing to be bound by theory, it is presentlybelieved that in addition to the aluminum oxide hydrates (the primarycomponent of the bauxite ore), that the other constituents probably playan important role in the sequestration of pollutants, either throughadsorption or chemical bonding or through sequestration in the varyingmineralogical structure of the constituents.

EXAMPLE 3

The tests of Examples 1 and 2 are repeated for bauxite, magnetite,goethite, and hematite, except that mercury is used as the pollutant ata concentration of 10 μg/L, 20 μg/L, and 40 μg/L. Mercury is removed inthese tests.

Microorganisms

Bauxite and allied mineral ores (e.g., copper, manganese, or titaniumores) are expected to be effective in adsorbing and inactivatingpathogenic microorganisms that may be encountered in soil, water, or airenvironment. Therefore, these ores can be used for applications, such as(for example):

-   1. Protection of drinking water supplies through:-   (a) installation of a subsurface mineral ore barrier in the path of    a migrating pathogen plume; or-   (b) running the extracted water at a drinking water plant through a    cartridge consisting of the mineral ore.-   2. Protection of indoor air from atmospheric releases of microbial    pathogens by installing a mineral ore cartridge in the heating,    ventilation, and air conditioning.-   3. Controlling the spread of the microbes in soil by mixing granular    or powdered ore with soil.

Most pathogenic microorganisms (e.g. bacteria and viruses) arenegatively charged under natural environmental conditions. The state ofcharge of the microorganism (e.g. a virus) is expressed by a quantityknown as the isoelectric point. This point is the value of pH at whichthe virus has a net charge of zero. The isoelectric points of HepatitisA, Polio, Reovirus 3, and Coxsackie A21 are 2.8, 3.8, 3.9, and 4.8,respectively. Under normal environmental conditions, bauxite and otherminerals (like Al, Cd, Mn ores and minerals) generally carry a positivecharge. The point of zero charge of bauxite generally occurs between apH of 7.53 and 8.29, depending on the electrolyte concentration. Thepoint of zero charge of other mineral oxides are: α-Al₂O₃, γ-AlOOH, CuO,α-Fe₂O₃, are 9.1, 8.2, 9.4, and 8.6, respectively. These oxides,hydroxides, and other mixture of minerals are known for their oxidizingproperties. Viral inactivation covers a wide range of phenomena, frommild, reversible inactivation (e.g., by non-specific sorption on quartzsand) to severe, irreversible fragmentation of viral proteins by lysis(e.g., exposure to strong oxidants, chemisorption, etc.). Coordinationof carbonyl groups from peptide linkages of sorbed viruses at themineral surfaces may provide a conduit of electron transfer. Viraldie-off may occur in the presence of active chemical sites on thesebarrier materials by a variety of mechanisms, including:

-   (i) disruption of the virus membrane;-   (ii) blockage of the receptor-ligand interactions essential for    infectivity;-   (iii) inhibition of the replication of pathogens; or-   (iv) alteration of the environment and reduction of the    susceptibility of infection.

Typically, in practice the emissions of power plants, industry, medicalfacilities, homes, or other point sources are contacted with the mineralores described herein so that the pollutants in the emissions areadsorbed, absorbed, chemically reacted, or otherwise inactivated.

In one embodiment of the invention, a gas stream containing pollutantmetals passes through a bed of granular bauxite (see FIG. 1). Anessential ingredient of the current invention for the application to gasstreams is the presence of sulfur. The geochemical complexation in thesesolid-phase surfaces generates sufficient sulfide/bisulfide toprecipitate contaminants metals as insoluble sulfides for long-termremediation of impacted sites. The thermodynamic parameters of the metalsulfides are given in Table 3. The low value of solubility product ofmetal sulfides indicates that these sulfides are very insolublecompound. Also, considering the Gibbs free energy (ΔG) values of thesemetal sulfides, the net change in free energy reactions indicate thatthe reactions are thermodynamically favorable.

TABLE 3 Thermodynamic parameters of metal sulfide precipitatesEquilibrium Solubility Gibbs energy constant of product of of formation*formation* metal sulfide Metal sulfide (ΔGf) Kcal/mol (log Kf) (Ksp)Arsenic(III) sulfide −40.269 24.466 (As2S3) Chromium sulfide (CrS)−32.893 24.111 Cadmium sulfide (CdS) −34.868 25.559 8 × 10-7  Copper(II)sulfide (CuS) −13.440 9.851 6 × 10-16 Mercury(II) sulfide (HgS) −11.1878.200 4 × 10-33 Nickel(II) sulfide (NiS) −21.462 15.732 Lead(II) sulfide(PbS) −23.097 16.930 3 × 10-7  *Temperature at 298.15 K.

The sequestration happens through one or more of the followingprocesses: surface oxidation, hydrolysis, surface catalyzedprecipitation, and/or incorporation by recrystallization andcoprecipitation. The bauxite is multi-functional in this environmentbecause it causes the removal of both positively charged (e.g., mercuryand/or selenium) and negatively charged (e.g., oxyanions of arsenic orchromium) of metals. Surface complexation reactions are responsible forremoval of both cationic and anionic species. A previous patent (U.S.Pat. No. 20010000475) has proposed the use of various catalysts forreducing SO2 to elemental sulfur, but the production of sulfides ismentioned as an “undesirable byproduct”. The current patent makes use ofthis sulfide production to co-precipitate out the pollutant metals.Unlike activated carbon, sequestration with bauxite is effective over awide range of temperatures ranging from below ambient to the hightemperatures encountered in combustion gases and incinerator exhausts.FIG. 2 shows the results of influent and effluent mercury measurementsin a simulated coal combustion gas stream flowing over a bed of bauxite.Bauxite in its natural form, crushed to −8+50 mesh size range was usedin this test. The presence of SO2 in the gas stream facilitates theco-precipitation of mercury as a sulfide.

In a second embodiment of the invention the bauxite is introduced in apowdered form into the gas stream. In the powdered form, the bauxite ismuch more reactive with the SO2 and metals. Also, injection of bauxitepowder can be implemented without increasing the pressure drop (andenergy requirement) in the flue gas equipment in a power plant. Themercury would be recovered along with the fly ash. In a fixed bed ofbauxite, additional pressure drop would be introduced into the flue gassystem, but the mercury can be recovered separate from the fly ash. Ineither case, the mercury is in a much less bio-available form.

In a third embodiment, the bauxite is modified to enhance itssequestration capability while retaining its essential character. Onemodification that enhances sequestration is wetting of the bauxitesurfaces with water. Other modifications include, but are not limitedto, hydroxyl, sulfonyl, thiol moieties associated with the surface.These functional groups improve the metal removal efficiency. Themodifications will be limited to simple processes, such as soaking thebauxite in solutions of acids, bases, or salts. Any heat treatment willinvolve milder temperatures (300° C.) or less compared to thetemperatures typically involved in manufacture of activated bauxite(400° C. or more).

In a fourth embodiment, the bauxite is applied in granular form as apermeable medium for the in situ treatment of groundwater (see FIGS. 3 aand b). Sulfur is not an essential ingredient in the sequestration ofpollutant metals in water or soil environments. Table 4 shows theresults of experiments conducted with groundwater containing mercury,arsenic, cadmium, and chromium. All these metals were substantiallyremoved by the bauxite.

TABLE 4 Treatment of metals in groundwater with bauxite Final InitialConcentration Barrier Target Concentration (ug/L) after 1 MaterialContaminant (ug/L)* day** Removal Bauxite Arsenic 25 <10 >60% −8+50Arsenic 50 <10 >80% mesh Arsenic 100 <10 >90% Arsenic 200 <10 >79%Arsenic 2,000 198 91% Bauxite Mercury 20 <0.5 >98% −8+50 Cadmium 1,000121 >87% mesh Chromium 1,000 <10 >99% Bauxite Arsenic 2,000 <10 >99%<200 mesh

Bauxite was among several adsorbents previously examined for possibleuse in water treatment (Saha, I., K. Dikshit, and M. Bandyopadhyay.Comparative Studies for Selection of Technologies for Arsenic Removalfrom Drinking Water. Proceedings of BUET-UNU International Workshop onTechnologies for Arsenic Removal from Drinking Water. Dhaka, Bangladesh,May 5-7, 2001), but it was eliminated after the first screening andsubsequent rounds of testing focused on materials that provided the muchhigher arsenic efficiency that would be required in a water treatmentunit installed in individual homes or drinking water plants forpoint-of-use treatment. This disenchantment with bauxite for home use isunderstandable because a very high efficiency, high capacity adsorbentis required that can remove arsenic from water within a few seconds orless of contact time available in home use systems. Others (U.S. Pat.No. 6,030,537) have tried to create special adsorptive materials withhigh adsorption efficiency, for example, by using a material calledactivated bauxite, in which bauxite is modified by heat treatment at 350to 700° C. Activated bauxite was tested by Itself and in combinationwith aluminum tri-hydrate by the said others. However, heat treatment isenergy intensive and expensive and is unnecessary for the currentinvention. In this embodiment of the current invention, where bauxite isapplied as a permeable medium for in situ treatment of groundwater, highefficiency and high capacity are not as important as easy availabilityand low cost. This is because groundwater flows very slowly (typically 1foot per day or less linear velocity). In this situation, the contacttime available to the water as it flows through the bauxite medium is ofthe order of several hours or days. Because the bauxite material ischeap, it can be installed as a treatment medium that is several feetthick in the path of the groundwater flow to provide the longer contacttimes and to provide moderately high sequestration capacity. Bauxite cantherefore be effectively applied in situations where slightly longercontact times can be arranged. Alternatively, in the current inventionthe reactivity of the bauxite may be modified or improved without heattreatment, for example, by soaking the bauxite in or wetting it with asolution of common acids, bases, or salts. This is a simpler and muchless expensive modification than heat treatment.

In a fifth embodiment, the bauxite is applied as a cap over contaminatedsediments under surface water bodies to prevent the migration of metalpollutants from the sediments to the water column above (see FIGS. 4 aand b). Table 5 shows the results of experiments conducted withsediments from two sources, New York Harbor and Sequim. In each case,bauxite removed the pollutant metals substantially.

TABLE 5 Sequestration of Mercury in Sediment by Bauxite Initial FinalFinal Concentration Concentration of Concentration of Removal Removal ofHg in Hg in Sediment Hg in Sediment Percentage of Percentage of SedimentSupernatant Supernatant Hg by Bauxite Hg by Bauxite Supernatant After 48Hrs After 96 Hrs After 48 Hrs After 96 Hrs Matrix (ug/L) (ug/L) (ug/L)(%) (%) New York 249.8 26.5 <0.20   89.39 >99.0 Harbor 243.5 31.2<0.20   87.19 >99.0 Sediment Sequim 256.5 57.5 <0.20   77.58 >99.0Sediment 251.4 53.4 <0.20   78.76 >99.0 Hg Control 241.2 237.8 238.1  N/A N/AIn a sixth embodiment, the bauxite is applied as a treatment forscrubber water exiting a power plant. In power plants that havescrubber, many of the heavy metals in the combustion gases are removedin the scrubber water and the water has to be treated before discharge.This water could be passed through a bed of granular bauxite.Alternatively, powdered bauxite could be added to the water and thenseparated out by settling or filtration.

In all these embodiments, bauxite, a relatively cheap sequestering agentis not regenerated and is applied as a single use reagent. This enhancesthe economic attractiveness of the treatment process. For example,during treatment of combustion gas streams, powdered bauxite is injectedinto the gas and the metals-laden bauxite is collected downstream withthe fly ash. The bauxite and the sequestered metals are disposed orreused according to the ongoing convention at the plant. The metalsbeing in a non-mobile, non-bio-available, sulfide form on the bauxitetheir subsequent potential leachability to the environment is verylimited. The waste product (e.g., fly ash) can therefore be safelyreused in a variety of products. In the case of treatment of groundwateror sediments, the bauxite can be permanently left in the environmentafter it has served its purpose.

While the forms of the invention herein disclosed constrate presentlypreferred embodiments, many others are possible. It is not intendedherein to mention all of the possible equivalent forms or ramificationsof the invention. It is to be understood that the terms used herein aremerely descriptive, rather than limiting, and that various changes maybe made without departing from the scope of the invention.

1. A method for treating water, sediment or soil containing pollutantsby the step of contacting pollutant-containing water, sediment,fractured rock or soil with a multi-functional sequestration agentcomprising bauxite in it relatively natural form, wherein said bauxiteis installed as a subsurface mineral ore barrier.
 2. A method fortreating water, sediment or soil containing pollutants by the step ofcontacting pollutant-containing water, sediment, fractured rock or soilwith a multi-functional sequestration agent comprising bauxite in itsrelatively natural form, wherein said bauxite is in a permeable barrier,and wherein said permeable barrier is installed in the path ofgroundwater flow.
 3. A method for treating water, sediment or soilcontaining pollutants by the step of contacting the pollutant-containingwater, fractured rock or soil with a multi-functional sequestrationagent comprising bauxite in its relatively natural form, wherein saidwater is groundwater.
 4. A method for removing or inactivatingmicroorganisms in an emission or in the environment comprisingcontacting the microorganisms with a mineral selected from bauxite,cooper ores, and mixtures thereof, wherein if the mineral is bauxite itis installed as a subsurface mineral ore barrier.
 5. A method forremoving or inactivating microorganisms in an emission or in theenvironment comprising contacting the microorganisms with a mineralselected from bauxite, copper ores, and mixtures thereof, wherein ifbauxite is used it is in a permeable barrier, which is installed in thepath of groundwater flow.
 6. A method for removing or inactivatingmicroorganisms in an emission or in the environment in groundwatercomprising contacting the microorganisms with a mineral selected frombauxite, copper ores, and mixtures thereof.